JPH0765712A - Manufacture of oxide cathode - Google Patents

Abstract

PURPOSE:To retain high reliability even in operation in high current density for a long time by heat-treating a cathode base metal in each atmosphere of nonoxidation property, oxidation property, and nonoxidation property in this order, and sticking an electron emissive material onto the base metal face. CONSTITUTION:A cathode base metal 11 of Ni alloy including a small amount of reducer is press-fitted in a cathode sleeve 15 consisting of nichrome alloy by press working, and it is welded with a laser. This is heat-treated in humidifying hydrogen, and is oxidized selectively for blackening the surface, and then three strip-shaped supports 16 are welded thereto, and it is welded the opening of a cylindrical cathode holder 17, thus a cathode structure is made. Heat treatment is performed for about ten minutes at 700-900 deg.C in nonoxidative atmosphere such as a hydrogen furnace, and next for about ten minutes at 700-850 deg.C in oxidative atmosphere such as air for relaxing the working distortion of the metal 11. Furthermore, it is heat-treated under the same condition as stated above in a hydrogen furnace so as to reduce the surface layer of the metal 11, and then an electron emissive material layer 12 is applied thereon, whereby it is completed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an oxide cathode used in a thermionic tube.

[0002]

2. Description of the Related Art Generally, in an oxide cathode assembly, as shown in FIG. 2, an alloy containing nickel as a cathode base metal 11 and a small amount of a reducing agent such as magnesium or silicon is used. The cathode base metal made of this alloy is press-molded into a desired shape and thickness and then bonded and fixed to the tip of the cathode sleeve. Then, an alkaline earth metal carbonate powder made of barium, strontium, calcium or the like, which becomes the electron-emitting substance layer 12, is applied onto the metal surface of the base by a spraying method or the like. This cathode structure is incorporated into an electron tube, and the carbonate is thermally decomposed in an exhaust step to form an alkaline earth metal oxide. This alkaline earth metal carbonate is a double salt or mixed salt of alkaline earth metal containing barium as a main component, but generally 57% by weight of barium, 39% by weight of strontium, and 4% by weight of calcium. The ternary carbonate which is a double salt of is widely used. Among these alkaline earth metal oxides, barium oxide contributes to electron emission. This barium oxide is a reducing agent magnesium that diffuses in the base metal during operation of the oxide cathode,
It is reduced at the boundary between the base metal and the oxide by silicon etc.,
For example, when magnesium is used as a reducing agent, free barium that contributes to electron emission is formed by the reaction of the following formula. BaO + Mg → Ba + MgO Therefore, in the oxide cathode, the reaction between the reducing agent and the oxide as the electron-emitting substance proceeds in the vicinity of the interface between the base metal and the oxide. Is formed.

By the way, in such a conventional oxide cathode, it is known that fine crystal grain layers 13 and 14 are formed in the vicinity of both surface portions of the cathode base metal 11, respectively. This fine crystal grain layer is formed by processing strain existing on the surface of the cathode base metal due to pressing or the like, wet hydrogen treatment for forming a black layer on the surface of the cathode sleeve, or oxidation from a carbonate of an electron emitting substance. It has been found to be related to the heating process for the decomposition reaction into substances. The fine crystal grain layer 14 which is not in contact with the electron emitting material layer 12 does not cause any problem because it has no particular influence on the electron emission performance, but the fine crystal grain layer 13 which is in contact with the electron emitting material layer 12 is the cathode substrate. It inhibits the diffusion of the reducing agent in the metal to the surface in contact with the electron emitting material layer, and significantly reduces the electron emitting ability.

As a method of removing this fine crystal grain layer,
Although a method of removing this fine crystal grain layer by cutting before applying the electron emitting substance, a method of chemically polishing, or the like has been proposed, it is difficult to completely remove it. Further, in the conventional oxide cathode, the generation of the fine crystal grain layer described above increases with the operation time, and in many cases, stable electron emission for a long time cannot be obtained. The reason is that oxygen dissociated from barium oxide in the electron emitting material during cathode operation reaches the fine crystal grain layer as a solid solution in the cathode base metal and promotes the growth of the still unstable fine crystal grain layer. Conceivable.

[0005]

The electron emission characteristics, especially the life characteristics of the conventional oxide cathode as described above depend largely on the amount of the fine crystal grain layer formed near the surface of the cathode base metal. ing. That is, the diffusion of the reducing agent in the base metal to the surface is hindered by the increase in the formation amount of the fine crystal grain layer and does not reach the base metal surface, so that the reaction between the reducing agent and barium oxide at the interface is reduced. However, the production of free barium is significantly reduced. Since the increase in the amount of formation of the fine crystal grain layer depends on the operation time and the emission current density, it becomes impossible to maintain the electron emission ability of high current density for a long time.

The present invention solves the above-mentioned disadvantages of the conventional method for producing an oxide cathode, and the method for producing an oxide cathode has little deterioration in electron emission characteristics even when operated for a long time at a high current density. The purpose is to provide.

[0007]

According to the present invention, a step of heat-treating a cathode base metal containing nickel as a main component and a small amount of a reducing agent added thereto in a non-oxidizing atmosphere, and then oxidizing the cathode base metal An oxide cathode comprising a step of heat treatment in an atmosphere, a step of heat treatment of the cathode base metal in a non-oxidizing atmosphere, and a step of subsequently depositing an electron emission layer on the surface of the cathode base metal. Is a manufacturing method.

[0008]

According to the present invention, the fine crystal grain layer near the surface of the cathode substrate metal can be made stable and strong, and as a result, the fine crystal grain layer can be formed with the operation time as seen in the conventional oxide cathode. It is possible to stably take out a high current density for a long time without increasing the formation amount. Further, in the process of heat-treating the cathode base metal in an oxidizing atmosphere, ultrafine irregularities are formed on the surface of the cathode base metal, and the adhesion strength with the electron emitting material layer is increased, so that the electron emitting material layer can be formed even during long-term operation. There is almost no danger of peeling.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. The oxide cathode assembly according to the present invention is shown in FIG.
It is configured as shown in. That is, the cathode base metal 11 made of a nickel alloy containing a small amount of a reducing agent obtained by rolling is sandwiched from the upper and lower surfaces and compressed by press working, so that the inner diameter of the cathode sleeve 15 made of a nichrome alloy can be closely fitted. It is made into a diametrical size and press-fitted into this cathode sleeve, and is joined and fixed by laser welding. Then, the cathode sleeve 15 is heat-treated in humidified hydrogen to be selectively oxidized to blacken the surface. Next, the three strip-shaped supports 16 are welded to the cathode sleeve, and this is welded to the opening of the cylindrical cathode holder 17 to assemble the cathode assembly.

Then, in order to alleviate the processing strain of the cathode base metal 12, the temperature is reduced to 70 in a non-oxidizing atmosphere such as a hydrogen furnace.
Heat treatment is performed at a temperature in the range of 0 to 900 ° C., for example, 800 ° C. for about 10 minutes. Next, heat treatment is performed in an oxidizing atmosphere such as air at a temperature in the range of 700 to 850 ° C., for example, 780 ° C. for about 10 minutes. In this step, an oxide layer is formed on the metal surface of the cathode substrate, but the fine crystal grain layer (corresponding to 13 and 14 in FIG. 2) near the surface is also internally oxidized to some extent. Furthermore, in a non-oxidizing atmosphere such as a hydrogen furnace, 700 to 90
Heat treatment is performed at a temperature in the range of 0 ° C., for example, 800 ° C. for about 10 minutes to reduce the surface oxide layer of the cathode base metal. Finally, the electron emitter layer 12 is applied on the metal surface of the cathode substrate to complete the oxide cathode assembly.

An oxide cathode assembly thus assembled and, for comparison, a cathode assembly manufactured by a conventional method in which a heat treatment was performed at 700 ° C. for 10 minutes in a hydrogen atmosphere to clean and then an electron emitting material was applied. Each was incorporated into a color cathode ray tube, the cathode was heated in the exhaust process to decompose the electron emitting substance from the carbonate to oxide, and after the exhaust pipe was chipped off, the cathode was activated in the aging process to complete the process. . Then, the electron emission characteristics of each cathode ray tube with long-term operation were measured.

FIG. 3 shows the result of a life test when the device was operated at a current density of 2.0 A / cm ² for a long time. The curve X shown in the figure is for the oxide cathode of the present invention, and the curve Y is for the conventional oxide cathode. As is clear from this characteristic comparison, the oxide cathode of the present invention has much less deterioration in electron emission characteristics due to long-term operation than the conventional oxide cathode, and the effect is more remarkable as the operation time increases. Is clear.

After the operation test for 10,000 hours, the cathode of the present invention was taken out from the cathode ray tube and the fine crystal grain layer near the surface of the cathode base metal was observed. As a result, the fine crystal grain layer found in the conventional cathode base metal was observed. Almost no increase was observed.

In the above-mentioned embodiment, 800 ° C. and 10 ° C. are used in a hydrogen atmosphere in order to reduce the working strain of the cathode base metal.
Although the case of performing the heat treatment for 1 minute was explained, when the treatment temperature is lower than 700 ° C., the relaxation of the working strain of the cathode base metal is not sufficient, the fine crystal grain layer is often generated, and the initial characteristics are not a problem. there were. Further, when the processing temperature is higher than 900 ° C., the generation of the fine crystal grain layer is reduced,
This is a problem because the selective oxidation layer of the cathode sleeve is decolorized and the mechanical strength of other cathode constituent materials is lowered. From these, the optimum temperature range was 700 ° C. to 900 ° C. as described above.

The heat treatment temperature in an oxidizing atmosphere for forming a stable and strong fine crystal grain layer is insufficient if the treatment temperature is lower than 700 ° C. Met. Further, when the treatment temperature was higher than 850 ° C., the formation position of the fine crystal grain layer became deep and the generation of vertical grain boundaries became remarkable. Further, there is a problem in that the cathode constituent materials other than the cathode base metal, for example, the strip-shaped support becomes significantly oxidized and the mechanical strength is lowered. From these, the heat treatment temperature in the oxidizing atmosphere is 700 as described above.
The optimum range was from ℃ to 850 ℃.

Furthermore, if the heat treatment temperature in the hydrogen atmosphere for reducing the surface oxide layer of the cathode base metal and other cathode constituent materials is lower than 700 ° C., the reduction is insufficient and the oxide remains. Further, if the heat treatment temperature is higher than 900 ° C., there is a problem that the selective oxidation layer of the cathode sleeve is discolored and the mechanical strength of other cathode constituent materials is lowered. Therefore, the heat treatment temperature is 700 ° C. to 9 ° C. as described above.
The range of 00 ° C was optimal.

The oxide cathode of the present invention can be widely used not only for cathode ray tubes but also for other thermionic tubes. The electron emission layer may contain a small amount of scandium oxide, other oxides, or the like.

[0018]

As described above, according to the present invention,
It is possible to obtain a stable and highly reliable oxide cathode that is excellent in long-time operation at high current density.

[Brief description of drawings]

FIG. 1 is a sectional view showing a cathode assembly according to an embodiment of the present invention.

FIG. 2 is a partially enlarged view of a general cathode base metal part.

FIG. 3 is a life comparison characteristic diagram of the present invention and the conventional one.

DESCRIPTION OF SYMBOLS 11 ... Cathode base metal 12 ... Electron emission layer 15 ... Cathode sleeve

Claims (3)

[Claims] 1. Electron emission of an alkaline earth metal carbonate on the metal surface of the cathode base after press-molding a cathode base metal containing nickel as a main component and adding a small amount of a reducing agent to the cathode sleeve. In the method of manufacturing an oxide cathode assembly for depositing a physical layer, a step of heat-treating the cathode base metal in a non-oxidizing atmosphere, a step of heat-treating the cathode base metal in an oxidizing atmosphere, and then the A step of heat-treating the cathode base metal in a non-oxidizing atmosphere,
And then depositing the electron emission layer on the metal surface of the cathode substrate. 2. The treatment temperature in the heat treatment step in a non-oxidizing atmosphere is in the range of 700 to 900 ° C.
A method for producing an oxide cathode as described above. 3. The method for producing an oxide cathode according to claim 1, wherein the treatment temperature in the step of performing the heat treatment in an oxidizing atmosphere is in the range of 700 to 850 ° C.